tetrachord Meaning, Definition & Usage

Tet"ra*chord noun
Etymology
L. tetrachordon, Gr. , from four-stringed; (see Tetra-) + a chord: cf. F. tétrachorde.
Definitions
  1. (Anc. Mus.) A scale series of four sounds, of which the extremes, or first and last, constituted a fourth. These extremes were immutable; the two middle sounds were changeable.

Webster 1913